Disc brake comprising at least one inclinable brake pad

ABSTRACT

The present invention mainly relates to a brake device for a motor vehicle, the brake device including a friction first element suitable for having a first face pressed against a first face of a second element which is secured to a wheel of the motor vehicle in order to slow said vehicle down, and an application third element for applying a braking force bearing via a first end against a second face of the friction first element that is opposite from the first face of the friction first element and suitable for pressing the friction first element against the second element, said brake device also including amplifier means for modifying the inclination of a tiltable plane containing the bearing surface between the friction first element and the application third element relative to a plane containing the first face of the second element.

The present invention relates mainly to a brake device for a motorvehicle, and to a brake system including such a device.

BACKGROUND OF THE INVENTION

A known type of brake device for a motor vehicle has a friction elementor “brake pad” suitable or being pressed under the action of a pistonagainst a brake disk that is constrained to rotate with a wheel of thevehicle.

The piston is in contact with a rear face of the brake pad in a planethat is substantially parallel to the plane of the brake disk.

The piston is moved towards the brake disk, e.g. by means of a hydraulicfluid under pressure or by means of an electric motor.

Document WO 98/14715 describes an electrical disk brake including anelectric motor for moving a piston towards a brake pad and for pressingthe brake pad against the brake disk when the brakes are applied. Thebearing plane in which the piston bears against the brake pad forms anon-zero angle with the plane containing the brake disk along a radiusof the brake disk, so that the bearing plane is tilted in the directionin which the brake disk rotates when the motor vehicle is traveling inthe forward direction.

Thus, when the brakes are applied, while the brake pad is being pressedagainst the brake disk, the braking force delivered by the electricmotor is amplified by a wedging effect to which the pad is subjectedbetween the brake disk and the piston, thereby offering assistance tobraking. The wedging effect is due to the torque exerted on the pad bythe disk due to said disk rotating, with the pad then being clampedbetween the disk and the face of the piston that bears against theslanting face of the pad.

The wedging effect, which is well known the in the field of brakes,makes it possible to amplify very considerably the braking force appliedto the piston. Unfortunately there is a risk of that phenomenon causingthe wheel to block, which is detrimental to the stability of thevehicle. In addition, such amplification is not necessary for low levelsof braking, and yet, in the example described in Document WO 98/14715,the amplification is present each time the brakes are applied.

OBJECTS AND SUMMARY OF THE INVENTION

An object of the present invention is therefore to offer a brake devicethat is effective and safe.

Another object of the present invention is to offer a brake device thatmakes it possible to obtain amplification that is controlled andvariable, in particular continuously variable amplification, in thebraking force delivered by applying the brakes.

Another object of the present invention is to offer a brake device thatis suitable for being adapted to all existing brake systems without itbeing necessary to make any special modifications to them, and to makeit possible to implement the functions of controlling the behavior ofthe vehicle by means of the brake system.

These objects are achieved by a brake device including a friction firstelement suitable for being pressed against a second element constrainedto rotate with the wheel of the vehicle, the first element being pressedagainst the second element by means of a third element bearing againstthe first element, said device also including amplifier means foramplifying the braking force exerted by the third element against thefirst element by using the wedging effect, said amplifier providing anamplification ratio that is variable.

In other words the braking force amplifier operates by the brake padbeing wedged in controlled and modifiable manner between the brake diskand the piston due to the torque to which the pad is subjected as itcomes into contact with the rotating brake disk, the wedging beingcontrolled by varying the angle of tilt of the bearing plane in whichthe piston bears against the pad relative to the plane containing thebrake disk.

The term “amplification” is used to mean making use of the kineticenergy of the vehicle for braking purposes.

The present invention mainly provides a brake device for a motorvehicle, the brake device including a friction first element suitablefor having a first face pressed against a first face of a second elementwhich is secured to a wheel of the motor vehicle in order to slow saidvehicle down, and an application third element for applying a brakingforce bearing via a first end against a second face of the frictionfirst element that is opposite from the first face of the friction firstelement and suitable for pressing the friction first element against thesecond element, said brake device also including amplifier means formodifying the inclination of a tiltable plane containing the bearingsurface between the friction first element and the application thirdelement relative to a plane containing the first face of the secondelement.

The present invention also provides a brake device, wherein the meansmake it possible for the inclination of the plane containing the bearingsurface between the friction first element and the application thirdelement to be modified continuously relative to the plane containing thefirst face of the second element.

The present invention also provides a device, wherein the first meansare constituted by a brake pad having a rigid support carrying thesecond face and a lining provided with the first face suitable forcoming into contact with a first face of the brake disk, and wherein thethird element includes a piston provided with the first face in contactwith the second face of the rigid support via the amplifier means and abraking force generator suitable for applying a braking force to thepiston.

The present invention also provides a device, wherein the braking forcegenerator is a master cylinder.

The present invention also provides a device, wherein the braking forcegenerator is an electric motor.

The present Invention also provides a device, wherein the braking forcegenerator is a hydraulic pump.

The present invention also provides a device, wherein the means comprisea first part that is mounted to pivot in the piston, in the first end ofsaid piston, and a second part mounted to pivot in the friction firstelement, in the second face of the friction first element, and whereinthe first and second parts are in mutual abutment respectively via firstand second plane faces, said faces being parallel to the tiltable plane.

The present invention also provides a device, wherein the first part issubstantially in the shape of a half-cylinder disposed in asemi-cylindrical cavity integral with the piston and wherein the secondpart has substantially the shape of a half-cylinder disposed in asemi-cylindrical cavity in the friction first element.

The present invention also provides a device, wherein the first part issubstantially in the shape of a half-sphere disposed in a hemisphericalcavity integral with the piston, and wherein the second part issubstantially in the shape of a half-sphere disposed in a hemisphericalcavity integral with the friction first element.

The present invention also provides a device, wherein the means furthercomprise friction-reducing means for reducing the friction betweenrespective ones of the first and second parts and respective ones of thefirst and second cavities, and also between the first and second facesof the first and second parts.

The present invention also provides a device, wherein thefriction-reducing means are ball bearings.

The present invention also provides a device, wherein the amplifiermeans are activated by an electric motor.

The present invention also provides a device also including a parkingbrake mechanism co-operating with the braking force amplifier means sothat the tiltable plane is tilted in the same direction as the gradienton which the motor vehicle is parked.

The present invention also provides a device including additional meansfor applying a braking force against the friction first element.

The present invention also provides a device, wherein the additionalmeans are resilient means exerting a force on the piston so as to pressthe friction first element against the second element in the event thatthe generator fails.

The present invention also provides a device, wherein the means alsomake it possible to press the friction first element against the secondelement.

The present invention also provides a device, wherein the assemblyformed by the first and second portions form a cam having a pivot axis.

The present invention also provides a device, wherein the assemblyformed by the first and second portions has a cross-section that issubstantially ellipsoidal.

The present invention also provides a brake system including anelectronic computer, a brake control suitable for being actuated by adriver, detection means for detecting when said brake control isactuated, and detection means for detecting the speed of at least onewheel, said brake system also including at least one brake device of thepresent invention, applied to said wheel, the amplifier means beingcontrolled by the electronic computer.

The present invention also provides a system, wherein the amplifiermeans of the device are activated when actuation of the brake control isdetected that corresponds to a level of deceleration greater than apredetermined value.

The present invention also provides a system, wherein the amplifiermeans are actuated for a deceleration value to be reached that isgreater than a predetermined value.

The present invention also provides a system, wherein the amplifiermeans are activated in the event that a necessity to decelerate saidwheel is detected.

The present invention offers the advantage of making it possible to usesmall-size brake elements whose small size is compensated by thecontrolled wedging effect between the brake disk and the brake pad.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be better understood on reading the followingdescription with reference to the accompanying drawings, in which:

FIG. 1 is a plan view of an embodiment of a brake device of the presentinvention;

FIG. 2 is a diagrammatic view in longitudinal section through a firstvariant of a device of the present invention in a first operating mode;

FIG. 3 is a diagrammatic view in longitudinal section through a firstvariant of a device of the present invention in a second operating mode;

FIG. 4 is a flow chart showing a first example of braking, implementinga brake device of the present invention;

FIG. 5 is a flow chart showing a second example of braking, implementinga brake device of the present invention;

FIG. 6 is a flow chart showing a third example of braking, implementinga brake device of the present invention;

FIG. 7 is a diagrammatic view in longitudinal section through a secondvariant embodiment of a device of the present invention;

FIG. 8 is a diagrammatic view in longitudinal section through a thirdvariant embodiment of a device of the present invention; and

FIG. 9 is a diagram of a brake system of the present invention.

MORE DETAILED DESCRIPTION

FIG. 1 shows a device of the present invention including a first element4 or brake pad provided with a first face 9 for application against asecond element 2 or brake disk that is constrained to rotate with awheel (not shown) of a motor vehicle, which wheel can be rotated in adirection A or in a direction B about an axis Z. The pad is providedwith a second face opposite from the first face, and typically butnon-limitingly, the two faces are mutually parallel.

The second face is carried by a rigid support 6, e.g. made of sheetsteel, and the application first face 9 is carried by a friction element8 having a coefficient of friction μ or by a lining fixed to the support6 by adhesive bonding and suitable for coming into contact with one face11 of the brake disk 2 when the brakes are applied, thereby slowing downthe speed of rotation of said brake disk. That face 9 of the lining 8which is suitable for coming into contact with the face 11 of the diskis contained in a plane P.

The pad is mounted to slide along an axis X perpendicular to the plane Pin a yoke 10 secured to a hub carrier of the vehicle.

Similarly, it is possible to imagine providing a pad that is mounted toslide in a brake caliper.

Advantageously, the device also includes two brake pads on either sideof the brake disk in two planes that are substantially parallel, eachpad being suitable for being pressed against an opposite face of thebrake disk when the brakes are applied.

The brake device of FIG. 1 also includes a “floating” caliper 14 mountedto move relative to the yoke 10 and mounted to slide about the yoke viacolumns 16.

Naturally, the brake device of the present invention is not limited to adevice including a caliper that is mounted to slide relative to a yoke,but rather it applies to any brake device making it possible to press atleast one brake pad against a disk brake.

FIGS. 2 and 3 show that the device of the present invention alsoincludes a third element 12 for applying a braking force against the padso as to press the brake pad against the brake disk.

The third means 12 for applying a braking force include a part referredto as a piston 13 that transmits the braking force and a generator GNfor generating a braking force. The brake piston 13 is mounted to slidein the caliper 14 that is mounted to slide along the axis X by means ofthe columns 16.

The piston 13 is substantially cylindrical and bears via a firstlongitudinal end 18 along the axis X against the rigid support 6 in aplane R. In FIG. 2, the plane R is parallel to the plane P. In FIG. 3,the piston bears against the rigid support 6 in a plane S forming anangle α with the plane R and along an axis Y perpendicular to thesection plane of FIGS. 2 and 3;

The piston 13 is subjected via a second longitudinal end 20 to a brakingforce EF exerted by the generator GN making it possible for the piston13 to press the pad 4 against the brake disk 2.

For example, the generator GN for generating the braking force is ahydraulic pump and is controlled by an electronic computer, or it is amaster cylinder actuated by a brake pedal 70 moved by the driver of themotor vehicle, sending a hydraulic fluid under pressure into the brakedevice, or else it is an assembly comprising a rotary electric motor M1and a nut and screw device making it possible for the piston to be movedaxially along the axis X towards the brake disk when the electric motoroperates.

The piston 13 bears against the pad 6 via means 22 having a firstportion 24 secured to the piston 13 and a second portion 28 secured tothe brake pad 6, the first portion bearing against the second portion inthe plane S, said plane S being mounted to pivot through an angle αabout the axis Y in a first or a second direction +θ, −θ, e.g. by anelectric motor M2 controlled by the electronic computer.

In the embodiment shown in FIGS. 2 and 3, the first portion 24 is in theshape of a half-cylinder or of a half-sphere 24′ mounted to pivot aboutthe axis Y in a corresponding semi-cylindrical cavity 26 orhemispherical cavity 26′ provided in the piston 13 via the first end 18.A rolling bearing 35, e.g. a ball bearing, is advantageously interposedbetween the first portion 24 and the cavity 26 in the piston.

The second portion 28 is also in the shape of a half-cylinder (or of ahalf-sphere 38′) mounted to pivot about the axis Y in a correspondingsemi-cylindrical cavity 30 (or a corresponding hemispherical cavity 30′)provided in an element (not shown) secured to the pad 6. A rollingbearing, e.g. a ball bearing 37 is advantageously interposed between thesecond portion 28 and the cavity 30 in the piston.

The element secured to the pad is advantageously disposed in a cavityprovided in the rigid support for supporting the brake pad, therebymaking it unnecessary to replace the means 22 when changing the brakepad.

Naturally, it is also possible to provide a cavity 26 in a separateelement mounted on the face 18 of the piston.

However, it is also naturally possible to provide a pad equipped with arigid support and in which the second portion 28 of the means 22 isdirectly mounted to rotate.

The first and second half-cylinders 24, 28 (or the first and secondhalf-spheres 24′, 28′) have respective plane ends 32, 34 via which theyare mounted to slide relative to each other in the tiltable plane S.

In the embodiment shown, a ball bearing or a roller bearing 39 isinterposed between the plane ends 32, 34.

The plane ends 32, 34 are parallel to the plane R when the means 22 arenot activated.

α advantageously lies in the range 0° to 5°, and preferably in the range0° to 4°.

Naturally, it is possible, without going beyond the ambit of the presentinvention to implement any other means making it possible to facilitatemovement of the half-cylinders 24, 28 (or of the half-spheres 24′, 28′)relative to each other, and pivoting of them in their respectivecavities 26, 30 (or 26′, 30′), e.g. by using self-lubricating materialsfor the means 22.

The present invention is also applicable to a brake device that can havea fixed caliper in which two pistons are mounted to slide on either sideof the brake disk and which is suitable, when the brakes are applied,for pressing each of the pads against a respective one of the oppositefaces of the reaction disk.

Below, consideration is given merely to a device having a single piston,but naturally the invention also relates to brake devices having two ormore pistons.

The yoke in which the pad slides along the axis X has structuralresilience symbolized in FIGS. 2 and 3 by a spring 36 of stiffness K1.

An explanation follows of how the brake device of the present inventionoperates.

In the operating mode shown in FIG. 2, the brake device operates as aconventional-type device. The plane S with which the plane ends 32, 34are parallel, and the plane R coincide, and therefore the plane S isparallel to the plane Q of the brake disk.

When a braking force EF is delivered by the generator GN on the secondend 20 of the piston 13, said piston slides along the axis X in thedirection indicated by arrow F, and moves the brake pad in translation,so that it comes into contact with the surface of the brake disk drivenin rotation about the axis Z in the direction A. Due to the brake diskmoving in rotation, the pad is subjected to torque E in the direction Adue to the yoke deforming elastically. In particular, the plane end 34of the second half-sphere 30 slides (or rolls) relative to the plane end32 of the first half-sphere.

The pad 6 in contact with the brake disk moves substantially laterallyin a plane parallel to the plane of the brake disk 2 under the action ofthe torque E and by the yoke deforming elastically.

In the operating mode shown in FIG. 3, the half-cylinders (or thehalf-spheres) have pivoted about the axis Y in the direction +θ, and theplane S then forms an angle α relative to the plane R about the axis Y.The brake disk is rotating in the direction A.

When a brake force EF delivered by the generator GN is exerted on thepiston 13, said piston moves along the axis X and drives the pad 6. Thepad 6 is pressed against the brake disk and is driven in the direction Aby the torque E. The pad 4 then moves laterally in a plane parallel tothe plane of the disk in the direction A, and in particular the planeend 34 of the second half-cylinder 30 (or of the second half-sphere)slides relative to the plane end 32 of the first half-cylinder (or ofthe first half-sphere). Due to the inclination of the plane S relativeto the plane of the brake disk, the pad 4 finds itself “wedged” betweenthe disk and the piston, and the braking force EF is then amplifiedproportionally to the angle α.

The brake device of the present invention advantageously co-operateswith measurement means for measuring the various parameters, such as,for example, the deformation DF of the yoke and/or the speed of thewheel and/or the displacement of a brake pedal causing a braking forceto be applied to the piston.

Measuring the deformation DF of the yoke makes it possible to quantifythe wedging effect and thus to regulate it by modifying the angle α.

Measuring the displacement of the brake pedal and in particular thespeed of displacement of said brake pedal, or measuring the forceapplied to the brake pedal makes it possible to determine whether thebraking desired by the driver corresponds to braking of high magnitude,i.e. to emergency braking, and thus to amplify the braking forcedelivered by the generator, e.g. by the driver, via a master cylinder orvia a hydraulic pump when an electrohydraulic brake system is used, bycausing the angle α to vary.

Since about 80% of braking actions correspond to deceleration of lessthan 0.3 G (the threshold below which power-assisted braking is notnecessary), it is possible, advantageously, to consider activating themeans 22 for amplifying the braking force only for a desireddeceleration greater than 0.3 G, for example.

The braking device of the present invention also makes it possible tomodify the ratio of amplification of the braking force exerted on thepiston during a regulation stage performed by a system for dynamicallycontrolling the path of the vehicle, e.g. in the event that a wheelblocks or that road-holding is lost.

FIG. 4 shows a first example of a flow chart of the various steps of abraking action implementing a brake system of the present invention. Forexample, the brake system is an electro-hydraulic or all-electricalbrake system. When the system is an electro-hydraulic brake system, amaster cylinder simulates, under normal operating conditions, how thebrake circuit reacts to the brake pedal, and the braking force appliedto the piston is exerted by brake liquid sent by an electro-hydraulicpump controlled by an electronic computer in response to thedisplacement of the brake pedal being detected.

When the system is an electrical brake system, an application electricmotor M1 applies a braking force to the piston, e.g. via a nut and screwassembly, the application motor M1 being actuated by an electroniccomputer in response to the displacement of the brake pedal beingdetected.

In the description below, when the term “braking force EF” is usedwithout any further specifications being given, it is a force exerted bya hydraulic or pneumatic fluid, or by an electric motor.

In step 102, a braking action AF is detected, e.g. by a stroke sensor 40disposed at the brake pedal. In step 104, the information is sent to anelectronic computer 42 which determines the value DS of the decelerationdesired by the driver.

In step 106, the computer compares the deceleration value DSn with athreshold value Vs.

It is possible to imagine providing a determined and non-modifiablevalue Vs or a value Vs modified by the electronic computer as a functionof the traffic conditions.

In the description below, the reference DSn designates the first valueof DS measured, and the reference DSn+1 designates the next value of DS.

If DSn is less than Vs, in step 108 the computer generates an order tothe force generator GN to exert a braking force EF on the piston.

In step 128, the computer verifies the variation of DS, by measuringDSn+1.

If DSn+1 is less than Vs, the method proceeds to step 130.

In step 130, the computer compares DSn+1 with DSn.

If DSn+1 is less than DSn, in step 132 the computer verifies whetherDSn+1 is equal to zero.

If DSn+1 is equal to zero, in step 134 the computer generates the orderto the pressure generator GN to cease exerting the braking force EF.

If DSn+1 is not equal to zero, in step 136 the computer generates theorder to modify EF in order to adapt the braking to the desireddeceleration level DSn+1, and then the method returns to step 108.

If DSn+1 is greater than DSn, the method proceeds to 108.

If DSn+1 is greater than Vs, the method proceeds to 110.

The description below involves DSn but also applies to DSn+1 coming fromstep 128.

If DSn is greater than Vs, the method proceeds to step 110.

In step 110, the computer generates an order to the force generator GNto exert a braking force EF on the piston and to the means 22 to causethe plane S to pivot about the axis Y through an angle α determined bymeans of the models entered in the memory of the computer 42.

In step 112, means for detecting the stability of the wheel, e.g. asensor 46 for sensing the deformation of the yoke and/or a sensor 48 forsensing the speed of the wheel 48, transmit their measurements to thecomputer 42 which determines whether there is a risk of the wheelsblocking, the sensors 46 and 48 are advantageously associated so thattheir measurements can be correlated.

If no risk of blocking is detected, in step 116, the computer instructsthe electric motor to reduce the angle α, and if the wedging angle α isnot sufficient, the computer instructs the generator GN to reduce thebraking force on the piston 13. This is performed in a plurality ofsteps in which the risk of the wheels blocking is verified and in whichthe angle α is modified.

If there is no risk of blocking, the braking is continued in step 114.

In step 120, the computer determines a new value for DS, DSn+1 with thedetection means disposed at the brake pedal, and compares DSn+1 withDSn.

If DSn+1 is greater than DSn, in step 122 the computer instructs themeans 22 to increase the angle α, and the risk of the wheel blocking isverified simultaneously in step 112.

If DSn+1 is less than DSn, in step 124 the computer verifies whetherDSn+1 is equal to DSn.

If DSn+1 is equal to DSn, in step 123 the computer generates the orderto the means 22 to maintain the angle α.

If DSn+1 is different from DSn, at 118 the computer verifies whetherDSn+1 is zero.

If DSn+1 is zero, in step 126 the computer generates the order to themeans 22 to reduce α to zero, and to the generator GN to reduce thebraking force EF to zero.

If DSn+1 is not zero, in step 127 the computer generates the order tothe means 22 to modify α, and then the method proceeds to step 120.

FIG. 5 shows the flow chart corresponding to the brake system operatingwithout action on the brake pedal being detected, when the need to slowdown at least one wheel, is detected, e.g. by means disposed at thewheels and/or on the body of the motor vehicle, for example when thewheel lacks grip or when an obstacle is detected requiring the vehicleto slow down in order to avoid impact between the vehicle and theobstacles.

The detected deceleration value is referred to as the “necessarydeceleration value DN” that is necessary for correcting the path of thevehicle.

In step 202, various parameters are measured, e.g. the speed of rotationof the wheels, the path that the vehicle is to follow, as a function ofthe position of the steering wheel and the distances at which theobstacles around the vehicle are situated, and said parameters aretransmitted to the computer.

In step 204, the computer determines whether one or more wheels shouldbe slowed down.

If no wheel needs to be slowed down, the braking stage ends at 212.

In step 206, the computer determines the necessary deceleration levelDN.

If DN is less than a predetermined deceleration value Vx, in step 208the computer generates an order to a generator GN to apply a brakingforce to the piston, and then the method proceeds to step 202 in orderverify whether the situation is normal again.

If DN is greater than Vx, in step 210 the computer generates an order tothe generator to apply a braking force to the piston 13 and to the means22 to increase the angle α by causing the plane S to pivot, and moreprecisely by causing the first and second pivotally mounted portions 24,28 to pivot in the cavities 26, 30.

Then the method returns to the step 202 for the purpose of monitoringthe effect of the braking actions, and, if necessary, to cause one ormore wheels to slow down again.

FIG. 6 shows a flow chart of how a conventional hydraulic brake systemoperates, in which system the pedal being depressed causes brake liquidto be sent under pressure from the master cylinder to the brake devicesplaced at the wheels. The situation described corresponds to anemergency braking situation.

In step 302, the speed of displacement of the brake pedal and/or theforce applied to the brake pedal H is measured Hn.

In step 304, the computer compares the value(s) H with predeterminedvalues Hs.

If Hn is less than Hs, the braking action is normal, and the flow chart140 then applies (flow chart shown in FIG. 4).

If Hn is greater than Hs, the braking action is then treated as beingemergency braking, and the computer generates the order to closesolenoid valves interrupting communication between the master cylinderand the brake devices, which corresponds to the step 308.

In step 310, the computer generates the order to the means 22 toincrease the angle α.

In step 312, the parameters making it possible to evaluate the stabilityof the wheel equipped with the brake and therefore the stability of themotor vehicle, e.g. the parameters of wheel rotation speed, and of yokedeformation, are measured and the risk of the wheels blocking isverified in step 313, the step being the equivalent of the step 112 inthe flow chart of FIG. 4.

In step 314, the computer compares a new value of H, Hn+1 and comparesHn+1 with Hn.

If Hn+1 is less than Hs, it is the step 140 that applies (see FIG. 4).

Otherwise, it is the step 308 that applies.

However, it is also possible to make provision for there to be nosolenoid values separating the master cylinder from the braking devicesand for the computer also to manage the effects of the braking actionstaken by the driver on the braking of the vehicle.

Naturally, the operating flow charts shown in FIGS. 4, 5 and 6 are givenmerely by way of example, and are in no way limiting. In addition, theyare suitable for being applied simultaneously, in which case they aremodified to make it possible for good co-operation to be establishedbetween them without the various actions interfering with one another.

Naturally, the examples of operating flow charts are not limiting andthe person skilled in the art is capable of modifying them and adaptingthem to solve problems in which the brake device of the presentinvention can contribute to providing a solution.

FIG. 7 shows a second embodiment for which the amplifier means 22 alsomake it possible to improve the operating safety of an electrical brakedevice.

The device has a braking force generator GN formed, for example, by amotor M1 applying a braking force to the piston 13 during a brakingstage in order to press at least one brake pad against the brake disk.

The amplifier means 22 are interposed between the piston and the pad.

The brake device also has additional application means 50 for pressingthe brake pad against the disk in the event that the generator GN or M1fails.

For example, the application means comprise resilient means, e.g. aspring disposed between the piston and a fixed element upstream from thepiston along the axis X.

In the event that the motor M1 fails, the spring 50 is released and itpresses at least one brake pad against the brake disk. The means 22, andin particular the motor M2 pivot the half-cylinders (or half-spheres) soas to amplify the braking force applied by the spring.

It is also possible to imagine making provision for the additionalapplication means 50 to apply a small but continuous braking force,enabling the disk to be “wiped” by the pad. Naturally, this is possibleonly if the residual torque does not prevent the motor vehicle fromoperating properly.

It is also possible to make provision to omit the generator forgenerating a braking force proportional to the desired braking, e.g. anelectric motor or a hydraulic fluid under pressure, to have the disk“wiped” continuously by at least one pad, and to regulate the level ofdeceleration by using the means 22 only.

FIG. 8 shows a detail of a fourth embodiment of the brake device of thepresent invention including means 22 forming the generator GN forgenerating a braking force EF and the amplifier for amplifying saidbraking force.

The first and second portions 24, 28 are of shapes making it possible,as they pivot, to bring the pad 4 towards the brake disk 2.

For example, the first and second half-cylinders (or the first andsecond half-spheres) form a cam of axis Y′ different from the axis Y anddisposed in a recess of substantially circular section, the recess beingformed by a first semi-cylindrical (or hemispherical) cavity carried byan element that is fixed relative to the brake pad and by a secondsemi-cylindrical (or hemispherical) cavity provided directly in therigid support 6 of the pad or in an element secured to said pad, butnevertheless capable of being disunited from the pad while the brake padis being changed.

It is also possible for the assembly formed by the first and the secondportions 24, 28 to be of substantially ellipsoid shape about the axis Yor about the axis Y′ so as also form a cam as shown in FIG. 8.

Thus, for example, when a detection of a braking action is transmittedto the computer, said computer gives the order to the motor 22 to pivotthe cam, thereby moving the pad away from the fixed element, and thuspressing the pad 4 against the brake disk 2, and also amplifying thebrake force exerted by the cam against the pad by a wedging effect.

This particular embodiment offers the advantage of being particularlycompact.

It is also possible to imagine a brake device of the present inventionthat can be used as a parking brake and including means for applying abraking force continuously when the vehicle is stationary, in compliancewith the legislation governing parking brakes, e.g. a Ball-In-Ramp (BIR)device which, when traction is applied to cables connected to the BIRdevice, e.g. by means of a parking brake lever disposed inside thevehicle, applies a braking force on the piston so as to press the padagainst the brake disk. The system controlling the means 22 includesmeans for detecting the gradient on which the motor vehicle is to beheld stationary.

When the parking brake is activated, the pads are pressed against thebrake disk, and the detection means detect the direction of the slope.On substantially horizontal ground, the computer generates an order tothe motor M2, if necessary, to amplify the braking force exerted by theparking brake means.

On sloping ground, the computer generates the order to the motor to tiltthe plane S in the same direction as the slope, thereby causing thebraking force to be amplified because the pad is subjected to torquefrom the brake disk in the same direction as the slope by means of thewedging effect appearing.

However, it is necessary to take account of the fact that the twohalf-cylinders (or the two half-spheres) roll slightly relative to eachother when the means 22 are actuated, and thus the stop position ismodified by the value of the rolling in the means 22.

The present invention offers the advantage of making it possible to usebraking force generators that are lower in power, since the brakingforce is amplified by the means 22, which is particularly advantageousin electrical brake devices.

The motor used to pivot the half-spheres or half-cylinders must enablethem to be pivoted rapidly so as to adapt the angle α to the brakingsituation and also so as to enable the brake pad to be disengaged whenthe amplification delivered by the means 22 is no longer desired.

Naturally, provision is made for all of the braking parametermeasurements to be taken at predetermined and advantageously regulartime intervals making it possible for the flow charts to be executedsubstantially continuously, if necessary.

A brake device is indeed obtained that includes means for amplifying thebraking force delivered by a generator, the amplification beingcontrolled and continuously variable.

The present invention is particularly applicable to the automobileindustry.

The present invention is applicable particularly to the brake industryfor motor vehicle brakes, and in particular to the brake industry forprivate motor vehicle brakes.

1. A brake device for a motor vehicle, the brake device including afriction first element suitable for having a first face pressed againsta first face of a second element which is secured to a wheel of themotor vehicle in order to slow said vehicle down, and an applicationthird element for applying a braking force bearing via a first endagainst a second face of the friction first element that is oppositefrom the first face of the friction first element and suitable forpressing the friction first element against the second element, saidbrake device also including amplifier means for modifying theinclination of a tiltable plane containing the bearing surface betweenthe friction first element and the application third element relative toa plane containing the first face of the second element.
 2. A brakedevice according to claim 1, wherein the means make it possible for theinclination of the plane containing the bearing surface between thefriction first element and the application third element to be modifiedcontinuously relative to the plane containing the first face of thesecond element.
 3. A brake device according to claim 1, wherein thefirst means are constituted by a brake pad having a rigid supportcarrying the second face and a lining provided with the first facesuitable for coming into contact with a first face of the brake disk,and wherein the third element includes a piston provided with the firstface in contact with the second face of the rigid support via theamplifier means and a braking force generator suitable for applying abraking force to the piston.
 4. A device according to claim 3, whereinthe braking force generator is a master cylinder.
 5. A device accordingto claim 3, wherein the braking force generator is an electric motor. 6.A device according to claim 3, wherein the braking force generator is ahydraulic pump.
 7. A device according to claim 1, wherein the meanscomprise a first part that is mounted to pivot in the piston, in thefirst end of said piston, and a second part mounted to pivot in thefriction first element, in the second face of the friction firstelement, and wherein the first and second parts are in mutual abutmentrespectively via first and second plane faces, said faces being parallelto the tiltable plane.
 8. A device according to claim 7, wherein thefirst part is substantially in the shape of a half-cylinder disposed ina semi-cylindrical cavity integral with the piston and wherein thesecond part has substantially the shape of a half-cylinder disposed in asemi-cylindrical cavity in the friction first element.
 9. A deviceaccording to claim 7, wherein the first part is substantially in theshape of a half-sphere disposed in a hemispherical cavity integral withthe piston, and wherein the second part is substantially in the shape ofa half-sphere disposed in a hemispherical cavity integral with thefriction first element.
 10. A device according to claim 7, wherein themeans further comprise friction-reducing means for reducing the frictionbetween respective ones of the first and second parts and respectiveones of the first and second cavities, and also between the first andsecond faces of the first and second parts.
 11. A device according toclaim 10, wherein the friction-reducing means are ball bearings.
 12. Adevice according to claim 1, wherein the amplifier means are activatedby an electric motor.
 13. A device according to claim 1, also includinga parking brake mechanism co-operating with the braking force amplifiermeans so that the tiltable plane is tilted in the same direction as thegradient on which the motor vehicle is parked.
 14. A device according toclaim 1, including additional means for applying a braking force againstthe friction first element.
 15. A device according to claim 3, includingadditional means for applying a braking force against the friction firstelement, and wherein the additional means are resilient means exerting aforce on the piston so as to press the friction first element againstthe second element in the event that the generator fails.
 16. A deviceaccording to claim 1, wherein the means also make it possible to pressthe friction first element against the second element.
 17. A deviceaccording to claim 7, wherein the means also make it possible to pressthe friction first element against the second element, and wherein theassembly formed by the first and second portions form a cam having apivot axis.
 18. A device according to claim 17, wherein the assemblyformed by the first and second portions has a cross-section that issubstantially ellipsoidal.
 19. A brake system including an electroniccomputer, a brake control suitable for being actuated by a driver,detection means for detecting when said brake control is actuated, anddetection means for detecting the speed of at least one wheel, saidbrake system also including at least one brake device according to claim1, applied to said wheel, the amplifier means being controlled by theelectronic computer.
 20. A brake system according to claim 19, whereinthe amplifier means of the device are activated when actuation of thebrake control is detected that corresponds to a level of decelerationgreater than a predetermined value.
 21. A system according to claim 19,wherein the amplifier means are actuated for a deceleration value to bereached that is greater than a predetermined value.
 22. A systemaccording to claim 19, wherein the amplifier means are activated in theevent that a necessity to decelerate said wheel is detected.